Visible indication of mistaken lamp use

ABSTRACT

A lamp includes an arc tube and a lighting unit for lighting the arc tube. The lighting unit includes a rectifier circuit, a smoothing circuit for partial smoothing, and an inverter circuit having a pair of switching elements. The smoothing circuit smoothes portions of the output voltage of the rectifier circuit below the first voltage value and outputs a voltage that falls between the first voltage value and the second voltage value. The discharge sustaining voltage of the arc tube is set to fall between the first and second values of the voltage Vdc output from the smoothing circuit.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 11/611,752 filed on Dec. 15, 2006, now Pat. No.7,701,153.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a 277V lamp having a light-emittingunit and a lighting circuit that is for lighting the light-emittingunit.

2. Description of Related Art

Conventional low-pressure discharge lamps have an arc tube and anelectronic lighting circuit for lighting the arc tube. Examples of suchlamps include self-ballasted fluorescent lamps (hereinafter, alsoreferred to simply as “lamps”). There are two types of lamps dependingon the rated lamp voltage. One is a 277V type designed for operation at277 volts. The other is a 120V type designed for operation at 120 volts.(Hereinafter 277V type and 120V type lamps are simply referred to as“277V lamps” and “120V lamps,” respectively.) Mainly, 277V lamps are foruse at commercial facilities and outdoors, whereas 120V lamps are foruse at home.

Lamps of the both types are similar in size and shape. Thus, it is oftenthe case that a 277V lamp is mistakenly used with a 120V lightingfixture (Such operation is improper and is also referred to as“misuse”).

Lamps of the both types are similar in size and shape. Thus, it is oftenthe case that a 277V lamp is mistakenly used with a 120V lightingfixture (Such operation is improper and is also referred to as“misuse”).

FIGS. 1 and 2 are circuit diagrams of lighting units employed inconventional lamps.

A lighting unit 901 illustrated in FIG. 1 includes a rectifier circuit903 for rectifying commercial low-frequency current voltage into directcurrent voltage, a smoothing circuit 905 for smoothing the rectifieddirect current voltage, an inverter circuit 909 for applying ahigh-frequency voltage to an arc tube 907. The rectifier circuit 903 iscomposed of so-called a bridge diode, whereas the smoothing circuit 905is composed of a smoothing capacitor 9C2.

The inverter circuit 909 includes two switching elements 9Q1 and 9Q2 andapplies a high-frequency voltage to the arc tube 907, by alternatelyswitching ON and OFF the two switching elements 9Q1 and 9Q2. Withapplication of the high-frequency voltage, the arc tube 907 emits light,so that high frequency power starts to be supplied to the arc tube 907.

The lighting unit 901 illustrated in FIG. 1 is connected to a commercialpower source via a base 902. Upon startup of the lamp operation, theelectric current output from the smoothing circuit 905 flows through theresistors 9R1 and 9R2 and then the capacitor 9C1. When the chargedvoltage of the capacitor 9C1 reaches a predetermined value, a triggerdiode 9TD2 breaks down and turns ON the switching element 9Q2.

Similarly to the lighting unit 901 illustrated in FIG. 1, a lightingunit 911 illustrated in FIG. 2 includes a rectifier circuit 913, asmoothing circuit 915, and an inverter circuit 917.

Upon startup of the lamp operation, the electric current output from therectifying and smoothing circuits flows through the resistors 9R3, 9R4,and 9R5. When the fraction of voltage obtained by the resistor 9R4reaches a predetermined value, the switching element 9Q3 is turned ON.

Although a 277V lamp and a 120V lamp differ in their rated lampvoltages, the respective lighting units are normally the same incircuitry. For this reason, even if a 277V lamp is mistakenly used for a120V lamp, the switching elements 9Q1 and 9Q2 still start to cause thelamp to emit light. In this case of misuse, the lamp manages to operatewithout flickering but with various problems. For example, the intensityof a 277V lamp mistakenly used for a 120V lamp is slightly lower thanthe intensity of a 120V lamp under normal operation. In addition, thelamp life is shorter than the rated lamp life.

Since a mistakenly used 277V lamp operates without flickering and otherimmediately noticeable problems, the user may not be able to recognizethat the 277V lamp is improperly used in place of a 120V lamp. With thisbeing a situation, there is a risk that the user has a wrong impressionthat the lower lamp intensity and shorter lamp life are simply due tothe bad quality of the lamp.

SUMMARY OF THE INVENTION

The present invention is made in view of the problems described aboveand aims to provide a 277V lamp for signaling users if the lamp ismistakenly used for a 120V lamp.

In order to achieve the above-described aim, the present inventionprovides a lamp of which rated voltage is 277 volts, that includes: alight-emitting unit including one or more light-emitting elements; andan electronic lighting circuit operable to light the light-emittingunit. When an effective source voltage is approximately 120 volts, thelight-emitting unit stays unilluminated for a period in each half cycleof alternating current voltage. The unilluminated period is longer thanan unilluminated period of the light-emitting unit when the effectivesource voltage is 277 volts.

The “unilluminated period” of the light-emitting unit in each half cycleof the alternating current voltage when the effective source voltage isapproximately 120 volts is longer than an unilluminated period of thelight-emitting unit when the effective source voltage is 277 volts.Thus, when the effective source voltage is approximately 120V, theunilluminated period of the light-emitting unit may be as long as theentire half cycle. In other words, when the effective source voltage isapproximately 120V, the light-emitting unit does not emit light at all.Note that the “alternating current voltage” used herein refers to avoltage fed from, for example, a commercial power source.

In addition, when the effective source voltage is 277 volts, “theunilluminated period” of the light-emitting unit in each half cycle maybe substantially equal to “0” seconds.

With the above structure, when the effective source voltage is 120V, thelight-emitting unit stays unilluminated for a longer time period in eachhalf cycle, as compared with a time period during which thelight-emitting unit stays unilluminated under normal operation at theeffective source voltage of 277V. This provides a visible indication tothe user of the lamp that the lamp for 277V operation is mistakenly usedwith a lighting fixture for 120V lamps.

As described above, misuse of the 277V lamp with application of 120V isnoticeable to the user because the lamp illuminates with annoyingflickers. This structure serves to discourage stealing of the lamp ofthe present invention for the purpose of using it with a householdlighting fixture for 120V lamps. This holds even if the lamp accordingto the present invention is used outdoors.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention, which are believed tobe novel, are set forth with particularity in the appended claims. Thepresent invention, both as to its organization and manner of operation,together with further objects and advantages, may best be understood byreference to the following description, taken in connection with theaccompanying drawings.

FIG. 1 is a circuit diagram of a lighting unit employed in aconventional lamp;

FIG. 2 is a circuit diagram of another lighting unit employed in aconventional lamp;

FIG. 3A is a view of a lamp 1 according to a first embodiment of thepresent invention, partly broken away to clearly show internal details;

FIG. 3B is a view of the lamp 1, partly broken away to clearly showinternal details;

FIG. 4 is a circuit diagram of the lamp 1 that includes a lighting unit7;

FIG. 5 is a chart illustrating the waveform of output voltage of asmoothing circuit;

FIG. 6 is a view illustrating variation in output voltages of thesmoothing circuit and an inverter circuit of the lamp 1 relative to asource voltage;

FIG. 7 is a view illustrating repetition of discharge and fading-outindicated by a region B in FIG. 6;

FIG. 8 is a chart of the waveform of a smoothed voltage Vdc output whenthe 277V lamp 1 is applied with the source voltage Vs of 120V;

FIG. 9 is a chart illustrating the waveform of output voltage of aconventional smoothing circuit 905;

FIG. 10 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo of a conventional lamp relative to the sourcevoltage Vs;

FIG. 11 is a chart indicating variation of the smoothed voltage Vdcoutput from a smoothing capacitor of a modification 1 when applied withthe source voltage Vs of 120V

FIG. 12 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo of a lamp according to a modification 2 relativeto the source voltage Vs;

FIG. 13 is a circuit diagram of a lamp 101 including a lighting unit 103according to a second embodiment 1;

FIG. 14 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo of the lighting unit 103 relative to the sourcevoltage Vs;

FIG. 15 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo of a lighting unit according to a modification 3relatively to the source voltage Vs;

FIG. 16 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo output from a lighting unit according to asecond embodiment 2 relatively to source voltage Vs;

FIG. 17 is a sectional view of a lamp according to the second embodiment2;

FIG. 18 is a circuit diagram of a lamp 201 including a lighting unit 203according to a third embodiment;

FIG. 19A is a circuit diagram of a lamp 241 that includes a lightingunit 245 according to a modification 4;

FIG. 19B is a circuit diagram of a lamp 271 including a lighting unit273 according to a modification 5;

FIG. 20A is a circuit diagram of a smoothing circuit 301 according to amodification 6;

FIG. 20B is a circuit diagram of a partial smoothing circuit 303according to a modification 7; and

FIG. 20C is a circuit diagram of a partial smoothing circuit 305according to a modification 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention which set forth the best modes contemplated to carry out theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be obvious toone of ordinary skill in the art that the present invention may bepracticed without these specific details. In other instances, well knownmethods, procedures, components, and circuits have not been described indetail as not to unnecessarily obscure aspects of the present invention.

With reference to the accompanying drawings, the following describesembodiments of the present invention directed to low-pressure dischargelamps of which rated lamp voltage is 277 volts. Note that the figuresare illustrated to facilitate the description of the present invention.Thus, the size, ratio, and other values may differ from those of anactual lamp.

<First Embodiment>

1. Overall Lamp Structure

FIGS. 3A and 3B illustrate a lamp according to a first embodiment of thepresent invention. FIGS. 3A and 3B are partly broken away to clearlyshow internal details.

As illustrated in FIGS. 3A and 3B, the lamp 1 includes an arc tube 3(equivalent to the low-pressure mercury discharge tube of the presentinvention) having a curved discharge path formed therethrough, a holder5 for holing the arc tube 3, a lighting unit 7 for lighting the arc tube3, and a case 11. The case 11 has a base 9 attached to one end andhouses the lighting unit 7 therein.

A tube body 13 of the arc tube 3 is composed of two U-shaped glass tubesconnected together in a manner to enclose space to be a discharge path.The tube body 13 has a pair of electrodes (not illustrated) sealed oneat each end 13 a and 13 b thereof. Naturally, the ends 13 a and 13 bcorrespond to the ends of the discharge path.

The tube body 13 of the arc tube 3 is formed in the following manner.First, two glass tubes (with outside diameter 12 mm, for example) eachof which is closed at one end and open at the other end are prepared.Each glass tube is bent into U-shape and bridge-connected to each otherat a position near the respective closed ends. The inner surface of thetube body 13 is coated with a phosphor layer.

Note that the tube body 13 may be additionally provided with aprotective layer formed between the inner surface and the phosphorlayer. In addition, the ends 13 a and 13 b of the tube body 13 areequivalent to the ends of the arc tube 3. Thus, the reference numerals“13 a” and “13 b” are also used to denote the ends of the arc tube 3.

Each electrode is composed of a filament coil and a pair of lead wiresacross which the filament coil is held. The electrodes are attached tothe tube body 13 by, for example, pinch-sealing the respective ends (13a and 13 b) of the tube body 13, with each filament coil inserted andrelatively positioned into the tube body 13.

Portions of the lead wires of each electrode are sealed at the end 13 aor 13 b of the tube body 13. In addition, the portions of each electrodeopposite to a respective filament coil extend from the end 13 a or 13 bof the arc tube 3 (tube body 13) as illustrated in FIG. 3A. In thefigure, the reference numerals “15 a” and “15 b” denote the lead wiresextending from the end 13 a, whereas “17 a” and “17 b” denote the leadwires extending from the end 13 b.

The distance between the electrodes (i.e. the filament coils) in thedischarge path (discharge path length) is, for example, 330 mm.

At the end 13 a of the tube body 13, a thin tube (not illustrated) isalso enclosed along with the electrode. The thin tube is used toevacuate the tube body 13 and to fill the tube body 13 with buffer gasand the like, after the electrodes are sealingly attached. The thin tubeis then sealed, for example, by chipping-off.

The arc tube 3 is filled, via the thin tube 19, with mercury (Hg) actingas a luminescent material, and a rare gas (for example, argon (Ar), neon(Ne) or a mixed gas of the two (Ar+Ne)) acting as a buffer gas.

The holder 5 is a bottomed tube having an end wall 5 b, which is thebottom, a cylindrical portion 5 c, and a tapered portion 5 a connectingthe end wall 5 b and the cylindrical portion 5 c. The tapered portion 5a is externally inclined in the direction away from the end wall 5 b.

The holder 5 is made of resin such as PET (polyethylene terephthalate).The end wall 5 b has insertion holes through which the ends 13 a and 13b of the arc tube 3 are inserted into the holder 5.

The arc tube 3 is held in place relatively to the holder 5, with theends 13 a and 13 b inserted into the holder 5 through the insertion holedescribed above and bonded to the inner surfaces of the holder 5 byadhesive (for example, silicon resin) 25.

Since the tapered portion 5 a of the holder 5 is thin, a plurality ofribs 14 are formed at circumferentially spaced locations.

The circuitry of the lighting unit 7 will be described later. Thelighting unit 7 includes a substrate 21 and a plurality of electroniccomponents 23 a, 23 b, and 23 c disposed and connected on the substrate21. Specifically, the electronic component 23 a, 23 b, and 23 c are acapacitor, a switching element, and a resistor, respectively.

The lighting unit 7 is attached to the holder 5, with the ribs 14supporting the main surface of the substrate 21 facing toward the arctube 3 and latching pawls (not illustrated) engaging the edges of thesubstrate 21.

The case 11 is in a funnel shape and has a small diameter portion 11 a,a large diameter portion 11 b, and an intermediate portion 11 c. Thelarge diameter portion 11 b is diametrically larger than the smalldiameter portion 11 a. The intermediate portion 11 c connects the smalland large diameter portions 11 a and 11 b and thus gradually extends indiameter from the small diameter portion 11 a toward the large diameterportion 11 b. The case 11 is made a resin, such as PBT (polybutyleneterephthalate).

To the inner circumferential surface of the large diameter portion 11 bof the case 11, the cylindrical portion 5 c of the holder 5 is attached.To the outer surface of the small diameter portion 11 a of the case 11,the base 9 is attached. In this embodiment, the large diameter portion11 b of the case 11 is fitted to cover the cylindrical portion 5 c ofthe holder 5.

The base 9 is, for example, so-called a screw base (Edison base)composed of a metal tube having a screw-threaded wall. It should benaturally appreciated, however, that the base 9 is not limited to thescrew base and may be a pin base, for example.

The lamp 1 according to the present embodiment includes a globe 27housing the arc tube 3 therein.

The globe 27 is made of, for example, glass or acrylic and has a D-typeshape. As illustrated in FIG. 3, the globe 27 has an open-end 27 a andthe rim of the open end 27 a is inserted in a circumferential clearanceformed between the large diameter portion 11 b of the case 11 and thecylindrical portion 5 c of the holder 5.

In this embodiment, the holder 5, the case 11, and the globe 27 areattached to one another through latching engagement and adhesion betweenthe holder 5 and the case 11. To be more specific, the holder 5 haslatching pawls 5 d formed on the edge of the cylindrical portion 5 c,whereas the case 11 has latching projections 11 d inwardly extendingfrom the inner surface thereof. The latching engagement is made betweenthe latching pawls 5 d of the holder 5 and the latching projections 11 dof the case 11. In addition, the adhesion between the holder 5 and thecase 11 is achieved with adhesive 29 supplied to fill the clearanceformed between the cylindrical portion 5 c of the holder 5 and the largediameter portion 11 b of the case 11. With this arrangement, the case11, the holder 5, and the globe 27 are fixed into a single piece.

Note that the case 11 has stoppers 11 e formed on the inner surfacethereof for preventing the holder 5 from sliding into the case 11 anyfarther. In addition, the plurality of latching pawls 5 d, latchingprojections 11 d, and stoppers 11 e are provided at circumferentiallyintervals on the holder 5 or the case 11. The total numbers of therespective components may be four, for example.

2. Circuitry of Lamp

FIG. 4 is a circuit diagram of the lamp 1 that includes the lightingunit 7.

The lighting unit 7 is composed mainly of a rectifier circuit 51, asmoothing circuit 53, an inverter circuit 55, a resonance circuit 57,and a preheating circuit 59.

The rectifier circuit 51 is for rectifying, which is a process ofconverting commercial low-frequency alternating current voltage(equivalent to the alternating current voltage of the present invention)into direct current voltage. The rectifier circuit 51 in this embodimentis of a full-wave rectification type and includes four diodesconstituting a bridge diode DB.

The smoothing circuit 53 is for smoothing the rectified direct currentvoltage. The smoothing circuit 53 in this embodiment is so-called apartial smoothing circuit and is composed of three diodes D1, D2, and D3and two smoothing capacitors C2 and C8.

The three diodes D1, D2, and D3 are serially connected, so that theforward direction of each diode coincides the direction from thenegative terminal toward the positive terminal of the rectifier circuit51. The smoothing capacitor C8 is connected between nodes N1 and N2. Thenode N1 is at the anode terminal of the diode D2, which is the secondone of the serially connected three diodes D1, D2, and D3. The node N2is at the positive terminal of the rectifier circuit 51. The smoothingcapacitor C2 is connected between nodes N3 and N4. The node N3 is at thecathode terminal of the diodes D2, which is the second one of theserially connected three diodes D1, D2, and D3. The node N4 is at thenegative terminal of the rectifier circuit 51.

For each of the smoothing capacitors C2 and C8, a capacitor having theelectrostatic capacity of 1.0 μF and the rated voltage of 450V isemployed. For each of the diodes D1, D2, and D3, a diode of the 1 A 400Vstandard is employed.

FIG. 5 is a chart illustrating the waveform of output voltage of thesmoothing circuit.

By connecting the diodes D1, D2, and D3 and the smoothing capacitors C2and C8 as illustrated in FIG. 4, the smoothing circuit 51 outputs toinverter circuit 55 partially smoothed direct current voltage asillustrated in FIG. 5. More specifically, the smoothing circuit 51converts the rectified voltage into direct current voltage by smoothingportions of the rectified voltage below a predetermined first voltagevalue V1. In this embodiment, the smoothing capacitors C2 and C8 areidentical in specifications. Thus, a second voltage value V2 illustratedin FIG. 5 is approximately equal to double of the first voltage valueV1.

Referring back to FIG. 4, the lighting unit 7 is connected to acommercial power source via the base 9. In addition, a resistor R1 and acoil NF1 are connected between the base 9 and the rectifier circuit 51,more specifically, to the negative terminal of the rectifier circuit 51.The resistor R1 is for suppressing rush current, whereas the coil NF1 isfor noise filtering.

The inverter circuit 55 is connected to the output terminal of thesmoothing circuit 53 and includes two switching elements. The switchingelements are alternately turned ON, so that a high-frequency voltage issupplied to the arc tube 3.

The inverter circuit 55 in this embodiment is of a so-called half-bridgetype and includes a pair of FETs Q1 and Q2 (which are equivalent to theswitching elements of the present invention) and two coupling capacitorsC5 and C7. For each of the coupling capacitor C5 and C7, a capacitorhaving the electrostatic capacity of 100 nF and the rated voltage of400V is employed.

A starting circuit composed of resistors R2, R3, and R4 starts up theinverter circuit 55 (i.e., switching of the FETs Q1 and Q2). The FETs Q1and Q2A are turned ON and OFF using the current transformer CT.

Now, the following describes the FETs Q1 and Q2, the starting circuit,and the current transformer CT.

The FETs Q1 and Q2 are both N-channel FETs. The FETs Q1 and Q2 areconnected in parallel to the smoothing circuit 53 with the source of theFET Q1 connected at a node N5 to the drain of the FET Q2. In addition,the drain of the FET Q1 and the source of the FET Q2 are connected tothe positive terminal and the negative terminal of the smoothing circuit53, respectively.

The resistors R3, R4, and R2 of the starting circuit are seriallyconnected in the stated order from the positive terminal of thesmoothing circuit 53. The node N5 between the FETs Q1 and Q2 isconnected to a node between the resistors R4 and R2.

The resistor R4 is connected to the current transformer CT at theterminal closer to the node N5. The current transformer CT includes oneprimary coil and two secondary coils and induces a voltage responsive tothe magnitude and direction of load current flowing through the primarycoil. In this embodiment, the primary coil of the current transformer CTis connected to the node N5 and the resonance circuit 57. In addition,each secondary coil is connected at one end to the gate of a differentone of the FETs Q1 and Q2 via nodes N6 and N7, respectively.

The resistor R3 is connected at one end to a node N6.

With the connection described above, when a voltage between the nodes N5and N6 reaches a set voltage value, the FET Q1 is turned ON to startswitching operation. Once the switching operation starts, the FETs Q1and Q2 alternately turned ON/OFF in response to the voltage induced inthe secondary coils of the current transformer CT.

More specifically, during the time the FET Q1 is ON, electric currentflows through a later-described choke coil L, the arc tube 3, and thelike to induce a voltage in the secondary coils. As soon as the FET Q1is turned OFF, the FET Q2 is turned ON. Similarly, the electric currentflowing during the time the FET Q2 is ON induces a voltage in thesecondary coils. As soon as the FET Q2 is turned OFF, the FET Q1 isturned ON.

Note that the resistors R2, R3, and R4 included in the starting circuitare a 440 kΩ resistor, a 7.8 MΩ resistor, and a 100 kΩ resistor,respectively.

The resonance circuit 57 is composed of the choke coil L and a resonantcapacitor C6 that are serially connected. The resonance circuit 57 feedspreheating current to the electrodes 14 and 16 (filament coils). Inaddition, the resonance circuit 57 amplifies the voltage across theelectrodes 15 and 16. For the resonant capacitor C6, a capacitor havingthe electrostatic capacity of 1800 pF and the rated voltage of 800V isemployed. For the choke coil L, a coil with an inductance of 2.3 mH isemployed.

The preheating circuit 59 includes a negative temperature coefficientresistor NTC connected in parallel to the electrode 16. The negativetemperature coefficient resistor NTC is for adjusting the electriccurrent supplied to the electrodes at the power feed starting time. Forthe negative temperature coefficient resistor NTC, a 22□ NTC numberedNTP05220LB1A0 (manufactured by Murata manufacturing Co., Ltd.) isemployed.

3. Lamp Operation at 277 Volts

FIG. 6 is a view illustrating variation in the output voltages of thesmoothing circuit and the inverter circuit relative to the sourcevoltage, measured during the time from the power feed start to theillumination start.

With reference to FIGS. 4 and 6, the following briefly describes thelighting operation of the lamp 1 and the variation in the lamp voltageduring the lighting operation. In this specification, the effectivevoltage fed to the lamp from the commercial power source is determinedas the source voltage.

The alternating current voltage fed from the commercial power source tothe lighting unit 7 via the base 9 is rectified by the rectifier circuit51 and then partially smoothed by the smoothing circuit 53. As a result,the direct current voltage partially smoothed as illustrated in FIG. 5is output to the inverter circuit 55.

The voltage output from the smoothing circuit 53 (hereinafter, simply“smoothed voltage Vdc”) increases with the source voltage Vs asillustrated in FIG. 6, until the switching element Q1 of the invertercircuit 55 is started. During the increase, the electric current (directcurrent) flows through the resistors R3, R4, and R2 of the startingcircuit.

With the increase of the source voltage Vs, the voltage between thenodes N5 and N6 increases and the voltage between the gate and source ofthe FET Q1 increases. When the source voltage Vs reaches a voltage valueVt illustrated in FIG. 6, the voltage between the gate and source of theFET Q1 reaches the threshold voltage (equally means the predeterminedvoltage mentioned above).

As a result, the inverter circuit 55 starts (more precisely, the FET Q1is turned ON) and the output voltage of the inverter circuit 55(hereinafter, simply “inverted voltage Vo”) increases sharply, asillustrated with a broken line in FIG. 6. The electric current (directcurrent) at this time momentary flows into the smoothing circuit 53 viathe FET Q1, the current transformer CT, the choke coil L, the electrode15, the resonant capacitor C6, the negative temperature coefficientresistor NTC, and the coupling capacitor C7. At this time, the couplingcapacitor C7 is charged.

As a result of the momentarily flowing electric current, a voltage isinduced in the secondary coil of the current transformer CT. The inducedvoltage raises the gate voltage of the FET Q1, so that the FET Q1 staysON. During the time the FET Q1 stays ON, the choke coil L and thecoupling capacitor C7 build up energy, so that the electric currentflowing through the current transformer CT eventually decreases.

With the decrease, the voltage across one of the secondary coils of thecurrent transformer CT connected to the FET Q1 decreases, so that theFET Q1 is turned OFF. On the other hand, the voltage across the othersecondary coil of the current transformer CT connected to the FET Q2increases. As a result, the gate voltage of the FET Q2 increases and theFET Q2 is turned ON.

As described above, the FETs Q1 and Q2 alternately repeats ON and OFF.At the same time, with the increase of the source voltage Vs, thesmoothed voltage Vdc and the inverted voltage Vo0 increase asillustrated in FIG. 6.

With the FETs Q1 and Q2 alternately tuned ON, electric current flowsthrough the electrodes 15 and 16 of the arc tube 3 to heat theelectrodes 15 and 16. During the time the FETQ1 is ON, electric currentflows through a closed circuit formed by the FET Q1, the currenttransformer CT, the choke coil L, the electrode 15, the resonantcapacitor C6, either of the electrode 16 and the negative temperaturecoefficient resistor NTC, and the coupling capacitor C5.

The resistance of the negative temperature coefficient resistor NTCvaries in accordance with the temperature change resulting from theelectric current flowing therethrough. Thorough the use of the variableresistance, the temperature of the electrodes 15 and 16 and theresonance frequency of the resonance circuit 57 are adjusted.

As a result, a dielectric breakdown occurs between the electrodes 15 and16 of the arc tube 3, as indicated by the point A in FIG. 6. Thus,electric current starts to flow across the electrodes 15 and 16, so thatthe lamp 1 is illuminated. At this time, the electric current (lampcurrent) flows through the arc tube 3, so that the inverted voltage Vosharply drops.

Thereafter, the lamp 1 repeats a cycle in which discharge is sustainedand then the discharge fades out, as indicated by the region B in FIG.6. During the repetition of discharge and fading-out, the invertedvoltage Vo and the smoothed voltage Vdc increase on the whole with theincrease of the source voltage Vs.

FIG. 7 is a view illustrating the repetition of discharge and fading-outindicated by the region B in FIG. 6.

As indicated by the region B, the inverted voltage Vo starts to risefirst. When the inverted voltage Vo reaches the point A1, a dielectricbreakdown occurs and thus discharge starts. Yet, since the invertedvoltage Vo is low at this stage, the discharge is unstable and cannot besustained. Eventually, the light goes out (fading-out of discharge).

In order to re-start discharge of the arc tube 3, the inverted voltageVo increases. When the inverted voltage Vo reaches the point A2, adielectric breakdown occurs again and discharge starts. Yet, theinverted voltage Vo is still low as described above. Thus, the dischargecannot be maintained and eventually fades out.

As described above, the cycle of discharge start, unstable discharge,and fading-out is repeated until the inverted voltage Vo increases andthe smoothed voltage Vdc increases to the voltage value Va illustratedin FIG. 6. The voltage value Va is the minimum level of the smoothedvoltage Vdc for allowing discharge to be stably sustained (hereinafterreferred to simply as “sustaining voltage value”). With the smoothedvoltage Vdc equal to or higher than the voltage value Va, the invertedvoltage Vo is high enough for stable discharge of the lamp 1.

Then, during the stably sustained discharge, the smoothed voltage Vdcand the inverted voltage Vo increase with the increase of the sourcevoltage Vs. Thus, the lamp 1 maintains stable discharge and operatesnormally, so that the intensity reaches a predetermined level when thesource voltage Vs is 277V.

4. Lamp Operation at 120 Volts

Next, a description is given of a case where the 277V lamp 1 having theabove structure is mistakenly used with a 120V lighting fixture.

Even when the lamp 1 designed to be operated at 277V is used with alighting fixture for a 120V lamp, the lighting unit 7 operates basicallyin the same manner with normal operation with a 277 lighting fixture. Itshould be noted however, that the source voltage Vs applied to the lamp1 is 120V.

The lighting unit 7 according to the first embodiment employs thesmoothing circuit 53 for partial smoothing. As illustrated in FIG. 6,the voltage output by the smoothing circuit 53 to the inverter circuit55 has been smoothed to fall between the first voltage value V1 and thesecond voltage value V2.

With the smoothing circuit 53, the discharge sustaining voltage Va fallsbetween first and second voltage values V1 and V2 when the sourcevoltage Vs is 120V.

FIG. 8 is a chart of the waveform of the smoothed voltage Vdc outputwhen the 277V lamp is applied with the source voltage Vs of 120V.

In FIG. 8, the first voltage value V1 is a reference value for partialsmoothing. The second voltage value V2 is the maximum voltage valueoutput from the rectifier circuit 51. As described above, the smoothingcapacitors C2 and C8 are identical, so that the first voltage value V1is about half the second voltage value V2.

Thus, when the smoothed voltage Vdc is equal to or higher than thesustaining voltage value Va, the discharge of the arc tube 3 issustained. On the other hand, when the smoothed voltage Vdc is below thesustaining voltage value Va, the discharge of the arc tube 3 fades out.

This is the condition where the lamp 1 repeats illumination andnon-illumination, thereby causing flickering noticeable to human eye.Signaled by such flickering, it is reasonably expected that the userwill realize that the 277V lamp 1 is mistakenly used for a 120V lamp.

Regarding the arc tube 3 according to the present embodiment, thedimensions including the glass tube diameter of the tube body 13 and theintra electrode distance are adjusted, so that the discharge sustainingvoltage Va falls between the first and second voltage values V1 and V2.

5. Comparison with Conventional Example

The following describes a 277V lamp (conventional example) having thelighting unit 901 illustrated in FIG. 1 is mistakenly used with a 120Vlighting fixture. The conventional lighting unit 901 in FIG. 1 isbasically identical to the lighting unit 7 illustrated in FIG. 4, exceptfor the smoothing circuit. Note that the lamp 1 according to the presentembodiment is referred to as a working example.

The conventional smoothing circuit 905 is for smoothing the entirepulsating-current voltage output from the rectifier circuit 903. On theother hand, the smoothing circuit 53 of the working example is a partialsmoothing circuit for smoothing portions of the pulsating-currentvoltage output from the rectifier circuit 903. (See FIG. 5).

FIG. 9 is a chart illustrating the waveform of output voltage of theconventional smoothing circuit 905.

The smoothed voltage Vdc of the conventional example is approximatelyconstant at the predetermined voltage value V3 throughout time t, asillustrated in FIG. 9.

FIG. 10 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo relative to the source voltage Vs, measuredduring the time from the power feed start to the illumination start.

When alternating current voltage is fed from a commercial power sourceto the lighting unit 901 via the base 902, the rectifier circuit 903rectifies the alternating current voltage and the smoothing circuit 905converts the rectified alternating current voltage into substantiallyliner direct current voltage, as illustrated in FIG. 9. The resultingdirect current voltage is then output to the inverter circuit 909.

The output voltage of the smoothing circuit 905 increases with thesource voltage Vs, as illustrated in FIG. 10. During this time, theelectric current (direct current) flows through the resistors 9R1 and9R2 and the capacitor 9C1 that are included in the starting circuit.

When the source voltage Vs reaches the voltage value Vt illustrated inFIG. 10, the switching element 9Q2 is turned ON to start the invertercircuit 909. Eventually, a dielectric breakdown occurs in the arc tube907 (at the point “A” in the figure).

Thereafter, the discharge and fading-out are repeated (indicated by theregion B in the figure). During the repetition, the smoothed voltage Vdcand the inverted voltage Vo increase with the source voltage Vs. Whenthe source voltage Vs reaches 120V, the smoothed voltage Vdc is equal toor higher than the discharge sustaining voltage Va, thereby allowingdischarge to be stably sustained.

As described above, even when mistakenly operated at the source voltageVs of 120V, the conventional example stably sustains discharge for awhile. This makes it difficult for the user to realize that the lamp isoperated improperly. As a consequence, it is likely that the user willmisunderstand that various problems occurred in due course are becauseof the inferior quality of the lamp.

6. Modification 1 of First Embodiment

According to the first embodiment described above, the lighting unit 7includes the smoothing circuit 53 for partial smoothing. In addition,the arc tube 3 and the smoothing capacitors C2 and C8 are so designedthat the discharge sustaining voltage Va falls between the maximum value(V2 in FIG. 5) and the minimum value (V1 in FIG. 5) of the smoothedvoltage Vdc.

With this structure, when the lamp 1 that is for operation at 277V ismistakenly used with a lighting fixture that is for 120V lamps, thesmoothed voltage Vdc output from the smoothing circuit 53 falls belowand rises above the discharge sustaining voltage Va. This causes the arctube 3 to repeat ON and OFF, which provides a noticeable indication tothe user that the lamp 1 is not operated normally.

Thus, the effect of the first embodiment is ensured as long as thelighting unit is structured to vary its output to repeatedly rise aboveand fall below the voltage value at which a discharge of the arc tube 3is stably sustained when the source voltage Vs is 120.

Thus, smoothing circuits other than the one for partial smoothing may beemployed. For example, a smoothing circuit may be a so-called activesmoothing circuit that is composed of one or more electrolyticcapacitors each with a small capacitance or that uses electric chargefed from the inverter circuit for smoothing.

The following describes a modification 1 of the first embodiment inwhich a smoothing circuit using small capacitance is employed.

FIG. 11 is a chart indicating variation of the smoothed voltage Vdcoutput from the smoothing capacitor of the modification 1 when appliedwith the source voltage Vs of 120V.

As illustrated in FIG. 11, the smoothed voltage Vdc output to theinverter circuit (55) falls between the first and second voltage valuesV1 and V2. Thus, if the discharge sustaining voltage Va of the arc tubealso falls between the first voltage V1 and the second voltage V2 asillustrated in FIG. 11, the discharge is sustained when the smoothedvoltage Vdc is equal to or hither than the discharge sustaining voltageVa. On the other hand, when the smoothed voltage Vdc is below thedischarge sustaining voltage Va, the discharge cannot be sustained andfades out.

That is to say, the smoothing circuit composed of a small capacitanceelectrolytic capacitor is capable of casing a lamp to repeat dischargeand fading-out, if the lamp is a 277V lamp mistakenly used for a 120Vlamp.

Specifically, to practice the modification 1, a 2.2 μF/450V capacitormay be employed as the smoothing capacitor.

7. Modification 2 of First Embodiment

In the case where the smoothing circuit 53 according to the firstembodiment described above is employed, fading-out of discharge occursif the first voltage value V1 of the smoothed voltage Vdc is below thedischarge sustaining voltage Va. In other words, the second voltagevalue V2 may be higher or lower than the discharge sustaining voltage Vaas long as the first voltage value V1 is below the discharge sustainingvoltage Va.

The following describes a modification 2 of the first embodiment. Themodification 2 relates to the case where the second voltage value V2 islower than the discharge sustaining voltage Va. Note that the firstembodiment above relates to the case where the second voltage value V2is higher than the sustaining voltage Va.

FIG. 12 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo of the lamp according to the modification 2relative to the source voltage Vs, measured during the time from powerfeed start to illumination start.

With the lamp 1 according to the modification 2, the first and secondvoltage values V1 and V2 of the smoothed voltage Vdc is set to fallbelow the discharge sustaining voltage Va when the source voltage Vs is120V.

Such setting is made by modifying the resonance circuit 57 illustratedin FIG. 4. More specifically, the inductance of the choke coil L is madesmaller and the capacitance of the resonant capacitor C6 is made larger,so that the inverted voltage Vo is lowered. Alternatively, the diameterof the arc tube and/or the length of the discharge path may be adjusted.

The following describes operation of the lamp according to themodification 2 by applying the source voltage Vs of 277V.

When the power feed to the lamp starts and the source voltage Vs reachesthe voltage value Vt, the inverter circuit (55) is activated. Thus, asillustrated in FIG. 12, the inverted voltage Vo increases sharply and adielectric breakdown in the arc tube (3) occurs (at the point A in FIG.12).

After the first dielectric breakdown, the lamp repeats discharge andfading-out until the first voltage value V1 of the smoothed voltage Vdcexceeds the discharge sustaining voltage Va (at the point C in FIG. 12).In FIG. 12, the region B indicates the repetition of discharge andfading-out. Flickering resulting from the repetition of dielectricbreakdown and discharge fading-out is more noticeable with the sourcevoltage Vs within in the range indicated as R1, and less noticeable withthe source voltage Vs within the range indicated as R2 in FIG. 12.

The range R1 is from the point at which the source voltage Vs reachesthe dielectric breakdown voltage Vb to the point D at which the secondvoltage value V2 reaches the discharge sustaining voltage Va. With thesource voltage Vs in the range R1, although a dielectric breakdown inthe arc tube (3) occurs, the discharge cannot be sustained but fades outimmediacy. This is because the smoothed voltage Vdc is lower than thedischarge sustaining voltage Va. The fading-out of discharge immediatelyafter deictic breakdown causes noticeable flickering.

The range R2 is from the point D at which the second voltage value V2reaches the discharge sustaining voltage Va to the point C at which thefirst voltage value V1 reaches the discharge sustaining voltage Va. Withthe source voltage Vs in the range R2, the second voltage value V2 ishigher than the discharge sustaining voltage Va. Thus, the lamp staysilluminated while the smoothed voltage Vdc is higher than the dischargesustaining voltage Va. With the source voltage Vs in the range R2,flickering is less noticeable (i.e. periods during which the lamp staysunilluminated are longer) than the flickering with the source voltage Vsin the range R1 described above.

As a consequence, if the lamp according to the modification 2 ismistakenly used with a 120V lighting fixture for, the source voltage Vsis similar to the 120V lamp as illustrated in FIG. 12. The sourcevoltage Vs of 120V falls within the range R1, thus the resultingflickering of the lamp is unnoticeable. That is to say, when mistakenlyoperated at 120V, the lamp according to the modification 2 flickersnoticeably as described above. This provides a noticeable indication tothe user that the lamp is not properly used.

Note that the lighting unit according to the modification 2 employs apartial smoothing circuit. Yet, a similar effect is achieved byemploying an active smoothing circuit described above in themodification 1.

<Second Embodiment>

According to the first embodiment, the smoothing circuit 53 is forpartial smoothing. According to a second embodiment of the presentinvention, however, discharge of the arc tube does not occur when thesource voltage is 120V.

(1) Switching Operation

The following describes a first example of the second embodiment(hereinafter, second embodiment 1) directed to a lamp of which switchingelements would not operate when the source voltage Vs is 120V.

FIG. 13 is a circuit diagram of a lamp 101 including a lighting unit 103according to the second embodiment 1.

The lighting unit 103 of the second embodiment 1 differs from thelighting unit 7 according to the first embodiment in a smoothing circuit105 and an inverter circuit 107.

The smoothing circuit 105 is composed of one smoothing capacitor 1C2. Inaddition, the inverter circuit 107 includes a starting circuit that iscomposed of resistors R2, R3, and R4 having different specificationsfrom the resistors used in the lighting unit 7. More specifically, theresistors 1R2, 1R3, and 1R4 in the inverter circuit 107 are such thatthe voltage between the gate and source of FET 1Q1 (the voltage betweennodes 1N5 and 1N6) is below the starting voltage when the source voltageVs applied is 120V.

In practice, a Zener diode 1ZD1 is serially connected between theresistors 1R3 and 1R4. Thus, the Zener diode 1ZD1 must be taken intoconsideration.

The following is a specific description of components including theresistors 1R2, 1R3, and 1R2.

The resistors 1R3, 1R4, and 1R2 in the starting circuit according to thesecond embodiment are a 7.8 MΩ resistor, a 100 kΩ resistor, and a 440 kΩresistor, respectively. The potential difference of the Zener diodes 1ZDis 0.3V. The starting voltage of the FETs 1Q1 and 1Q2 is 2.5V.

With the starting circuit employing the resistors 1R3, 1R4, and 1R2, theFETs 1Q1 and 1Q2, and the Zener diode 1ZD described above, the FETs 1Q1and 1Q2 start when the source voltage Vs is 129.7V.

FIG. 14 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo of the lighting unit 103 according to the secondembodiment 1 relative to the source voltage Vs, measured during the timefrom power feed start to illumination start.

As illustrated in FIG. 14, with the lighting unit 103 according to thesecond embodiment 1, the FET 1Q1 turns ON when the source voltage Vsreaches Vt, so that the inverter circuit 107 starts. With increase ofthe source voltage Vs, the inverted voltage Vo and the smoothed voltageVdc increase. As a result, a dielectric breakdown in the arc tube 3occurs and the lamp 101 emits light.

As described above, with the starting circuit composed of the resistorsand Zener diode having the above-described specifications, the FET 1Q1turns ON when the source voltage Vs is 129.7V or higher (Vt in thefigure). Since the voltage value Vt is higher than the source voltage120V, the lamp 101 cannot be lit if the lamp 101 is improperly used witha 120V lighting fixture. This provides a noticeable indication for theuser to make a check and realize that the 277V lamp is mistakenly usedfor a 120V lamp.

Note that the smoothing circuit according to the second embodiment 1 isfor full smoothing. Yet, similarly to the smoothing circuit 53 accordingto the first embodiment, a partial smoothing circuit may be employed.The following briefly describes a modification 3 according to which thesecond embodiment 1 is modified to employ a partial smoothing circuit,with reference to FIG. 15.

FIG. 15 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo of the lighting unit 103 according to themodification 3 relatively to the source voltage Vs, measured during thetime from power feed start to illumination start.

Even with a partial smoothing circuit, the value of the starting voltageat which the FET 1Q1 is turned ON is determined by the specifications ofelectronic components of the starting circuit including the resistorsR2, R3, and R4.

As long as the source voltage Vs at which the FET 1Q1 starts is higherthan 120V, the modification 3 achieves a similar effect as the secondembodiment 1.

(2) Illumination of Arc Tube

The following describes a second embodiment 2 according to which adielectric breakdown of the arc tube does not occur when the sourcevoltage Vs is 120V.

The lamp according to the second embodiment 2 includes a lighting unitthat is identical to the lighting unit 7 according to the firstembodiment. Difference with the first embodiment lies in the structureof the arc tube. The arc tube is so designed that a dielectric breakdownoccurs when applied with the source voltage Vs that is higher than 120V.

FIG. 16 is a chart indicating variations of the smoothed voltage Vdc andthe inverted voltage Vo output from the lighting unit 103 according tothe second embodiment 2 relatively to source voltage Vs, measured duringthe time from power feed start to illumination start.

As illustrated in FIG. 16, the FET (1Q1) starts when the source voltageVs reaches the voltage value Vt. When the source voltage Vs reaches thevoltage value Vt, the FET (1Q1) is turned ON.

With increase of the source voltage Vs, the smoothed voltage Vdc and theinverted voltage Vo increase. When the source voltage Vs reaches thedielectric breakdown voltage Vb, a dielectric breakdown in the arc tubeoccurs (at the point A in the figure). As a result, the arc tube startsto emit light and thus the inverted voltage Vo drops sharply.

Thereafter, the source voltage Vs increases to reach 277V, so that thelamp illuminates at the predetermined intensity in normal operation.

Next, a description of the lamp according to the second embodiment 2 isgiven.

FIG. 17 is a sectional view of the lamp according to the secondembodiment 2.

As illustrated in FIG. 17, a lamp 111 includes an arc tube 113 having adischarge path of a double spiral shape, a holder 114 for holding thearc tube 113, a lighting unit 112 for lighting the arc tube 113, a case11 having a base 9 attached to one end thereof and housing the lightingunit 112 therein. Note that the same reference numerals are used todenote components identical to those used in the lamp 1 according to thefirst embodiment.

The arc tube 113 has a tube body 115 having a double spiral shape and apair of electrodes (not illustrated) sealed one at each end 115 a and115 b of the tube body 115. The ends of the tube body 115 correspond tothe ends of the discharge path.

In this embodiment, the tube body 115 is composed of one glass tube(with the outside diameter of 9.0 mm, for example) having a bend at asubstantially middle thereof. Portions of the glass tube from the bend115 c toward the respective ends 115 a and 115 b are wound around animaginarily spiral axis A to form a double spiral.

Lead wires 117 a and 117 b sealed within the end 115 a of the tube body115 are connected to the lighting unit 112. Similarly, lead wires 119 aand 119 b sealed within the other end 115 b of the tube body 115 areconnected to the lighting unit 112.

The length of the discharge path formed through the arc tube 113 is 620mm, for example. In addition, the arc tube 113 is filled with mercury,buffer gas, and the like. A thin tube 121 is sealed at the end 115 a ofthe tube body 115 along with the electrode.

The ends 115 a and 115 b of the arc tube 113 are inserted into theholder 114 through the insertion holes in the bottom 114 b. With thisstate, the ends 115 a and 115 b are fixed to the inner surfaces of theholder 114 with adhesive (for example, silicon resin) 123, so that thearc tube 112 is secured to the holder 114.

The arc tube 113 differs from the arc tube 3 according to the firstembodiment in the following points including the glass tube outsidediameter, the discharge path length, types of the buffer gas (mixedratio), and the filling pressure. With this arrangement, the arc tube113 is so designed that a dielectric breakdown occurs when applied withthe source voltage Vs that is higher than 120V.

Similarly to the lighting unit 7 according to the first embodiment, thelighting unit 112 according to the second embodiment 2 includes apartial smoothing circuit. Alternatively, however, the lighting unit 112may include a full smoothing circuit similar to the lighting unit 103according to the second embodiment 1.

In addition, the electrode 15 of the arc tube 3 may be short-circuited(at the lead wires) as in the case of the lighting unit 103, so as notto preheat the electrodes. With this arrangement, the electrodes areheated only by the electric current flowing through the arc tube andthus flickering is made to occurs more notably.

<Third Embodiment>

The lamps 1, 101, and 111 according to the first and second embodimentsare all so-called low-pressure discharge lamps and each includes the arctube 3 or 113. According to a third embodiment of the present invention,a lamp 201 includes light-emitting elements (so-called LEDs) instead ofan arc tube.

FIG. 18 is a circuit diagram of the lamp 201 including a lighting unit203 according to the third embodiment.

The lamp 201 includes a light-emitting unit 205 composed of a pluralityof LEDs, a lighting unit 203 for operating (lighting) the light-emittingunit 205, and a base 9 for supplying electric power to the lighting unit203.

The light-emitting unit 205 includes a first LED array 215, a second LEDarray 225, and a capacitor 2C5 that are connected in parallel. The firstLED array 215 includes a plurality of serially connected LEDs 210, 211,212, and 213. The second LED array 225 includes a plurality of seriallyconnected LEDs 220, 221, 222, and 223.

In this embodiment, the LEDs 210-213 in the first LED array 215 areconnected to have the same forward direction. Similarly, the LEDs220-223 in the second LED array 225 are connected to have the sameforward direction. Yet, the first and second LED arrays 215 and 225 areconnected to have different forward directions.

The lighting unit 203 is mainly composed of a rectifier circuit 231, asmoothing circuit 233, and an inverter circuit 235.

Similarly to the rectifier circuit 51 according to the first embodiment,the rectifier circuit 231 is composed of a diode bridge 2DB. Thesmoothing circuit 233 is a full smoothing circuit composed of onesmoothing capacitor 2CD1. For the smoothing capacitor 2CD1, a capacitorwith the electrostatic capacity of 2.2 μF and the rated voltage of 450Vmay be employed.

The inverter circuit 235 is of a so-called half-bridge type composed ofa pair of transistors 2Q1 and 2Q2 (equivalent to the switching elementsaccording to the present invention) and two coupling capacitors 2C4 and2C6.

For each of the coupling capacitors 2C4 and 2C6, a capacitor with theelectrostatic capacity of 47 nF and the rated voltage of 250V may beemployed.

The starting circuit composed of the resistors 2R2, 2R1, and 2R0 startsthe inverter circuit 235, i.e., switching operation of the transistors2Q1 and 2Q2. In addition, ON and OFF of the switching is done by thecurrent transformer 2CT.

Now, the following describes the connection between the transistors 2Q1and 2Q2, the starting circuit, and the current transformer 2CT.

First of all, the emitter of the transistor 2Q1 is serially connected ata node 2N6 to the collector of the transistor 2Q2. The seriallyconnected transistors 2Q1 and 2Q2 are connected in parallel to thesmoothing circuit 233. That is to say, the collector of the transistor2Q1 is connected to the positive terminal of the smoothing circuit 233,whereas the emitter of the transistor 2Q2 is connected to the negativeterminal of the smoothing circuit 233.

The resistors 2R2, 2R1, and 2R0 included in the starting circuit areserially connected via the nodes 2N5 and 2N4 in the stated order fromthe positive terminal of the smoothing circuit 233. In addition, thenode 2N5 is connected to a node 2N6. The resistor 2R0 is connected inparallel to the capacitor 2C2.

The coupling capacitor 2C4 is connected at one end to the collector ofthe transistor 2Q1. In addition, the coupling capacitor 2C6 is connectedat one end to the emitter of the transistor 2Q2. The other ends of thecoupling capacitors 2C4 and 2C6 are serially connected to each other ata node 2N7.

Between the nodes 2N7 and 2N6, the current transformer 2CT, the chokecoil 2L, and the light-emitting unit 205 are serially connected. Inconjunction with the capacitor 2C5 connected in parallel to the LEDarrays 215 and 225, the choke coil 2L improves the waveform of theelectric current flowing through the LED arrays 215 and 225 (fromtriangular wave to sinusoidal wave, for example).

Similarly to the current transformer CT according to the firstembodiment, the current transformer 2CT is composed of one primary coiland two secondary coils. One of the secondary coils of the currenttransformer 2CT is connected to the node 2N6 and the base of thetransistor 2Q1. The other secondary coil is connected to the base andthe emitter of the transistor 2Q2.

With the connection as described above, when the voltage at the node 2N4reaches the predetermined voltage (i.e., the fraction of voltageobtained by the resistor 2R0 reaches the predetermined voltage), thetransistor 2Q2 is tuned ON to start switching operation. Then,responsive to the voltage induced in the secondary coils of the currenttransformer CT, the transistors 2Q1 and 2Q2 alternately repeats ON andOFF.

During the time the transistor 2Q2 is ON, the electric current outputfrom the smoothing circuit 233 flows through the coupling capacitor 2C4,the second LED array 225 of the light-emitting unit 205, the choke coil2L, the current transformer 2CT, and the transistor 2Q2, beforereturning back into the smoothing circuit 233.

On the other hand, during the time the transistor 2Q1 is ON, theelectric current output from the smoothing circuit 233 flows through thetransistor 2Q1, the current transformer 2CT, the choke coil 2L, thefirst LED array 215 of the light-emitting unit 205, and the couplingcapacitor 2C6, before returning back into the smoothing circuit 233.

According to the third embodiment, the specifications of the resistors2R2, 2R1, and 2R0 included in the starting circuit are determined sothat the transistor 2Q2 is turned ON when applied with the sourcevoltage Vs that is higher than 120V.

(1) Modification of Third Embodiment (Modification 4)

FIG. 19A is a circuit diagram of a lamp 241 that includes a lightingunit 245 according to a modification 4 of the present embodiment.

As illustrated in FIG. 19A, the lamp 241 according to the modification 4includes a light-emitting unit 243 and a lighting unit 245 for operatingthe light-emitting unit 243. Similarly to the third embodiment, thelight-emitting unit 243 includes a plurality of LEDs.

The light-emitting unit 243 includes LEDs 247, 248, and 249 seriallyconnected in a manner that all the LEDs have the same forward direction.

The lighting unit 245 includes a rectifier circuit 251, a smoothingcircuit 253, a starting circuit 255, and a feed circuit 257.

The rectifier circuit 251 and the smoothing circuit 253 are identical instructure to the rectifier circuit and the smoothing circuit accordingto the third embodiment. The feed circuit 257 includes means foradjusting the switching elements as well as the ON state of theswitching element. More specifically, the switching element is embodiedby the transistor 2Q3, and the adjusting means is embodied by the chokecoil 2L1.

When a predetermined condition is satisfied, the starting circuit 255turns ON the transistor 2Q3 of the feed circuit 257. The startingcircuit 255 is composed of the a Zener diode 2ZD, a resistor 2R5, and aresistor 2R4 connected in series in the stated order from the positiveterminal of the smoothing circuit 253.

The resistors 2R5 and 2R4 are connected via a node 2N8. In addition, theresistor 2R4 is connected in parallel to the capacitor 2C8.

Now, the following describes connection of the transistor 2Q3. Thetransistor 2Q3 is connected at the base to the node 2N8. The collectorof the transistor 2Q3 is connected to one end of the light-emitting unit243 via the choke coil 2L1. The emitter of the transistor 2Q3 isconnected to the negative terminal of the smoothing circuit 253.

The choke coil 2L1 includes one primary coil and one secondary coil. Asdescribed above, the primary coil is serially connected between thecollector of the transistor 2Q3 and the light-emitting unit 243. Inaddition, the secondary coil is connected to the node 2N8 (the base ofthe transistor 2Q3) and the emitter of the transistor 2Q3.

The electric current flowing through the primary coil of the choke coil2L1 is direct current output from the smoothing circuit 253. Theelectric current includes AC components generated in response to ON andOFF of the transistor 2Q3. Thus, the secondary coil induces voltagecorresponding to the AC components (ripples) of the electric currentfollowing in the primary coil. The transistor 2Q3 tunes ON and OFFresponsive to the induced voltage.

Note that capacitor 2C9 connected in parallel to the light-emitting unit243 composed of the serially connected LEDs 247, 248, and 249 smoothesthe electric current flowing through the LEDs 247, 248, and 249.

With the above-described connection, the voltage at the node 2N8 (i.e.,the fraction of voltage obtained by the resistor 2R4) satisfies thepredetermined condition (reaches the predetermined voltage value), thetransistor 2Q3 is turned ON. As a consequence, the electric current(direct current) out of the smoothing circuit 253 flows through thelight-emitting unit 243, the choke coil 2L1, and the transistor 2Q3, andthen returns back into the smoothing circuit 253.

At this time, the electric current flowing through the primary coil ofthe choke coil 2L1 includes the AC components and the voltagecorresponding to the AC components is induced in the secondary coils.With the induced voltage, the transistor 2Q3 repeats ON and OFF and thelight-emitting unit 243 stays illuminated by the energy built up in theprimary coil.

Also in the modification 4, the specifications of the resistors 2R5 and2R4 and the Zener diode 2ZD in the starting circuit are so determinedthat the transistor 2Q3 is turned ON when applied with the sourcevoltage Vs that is higher than 120V.

(2) Modification of Third Embodiment (Modification 5)

According to the modification 4, the transistor is turned ON and OFF inresponse to the fraction of voltage obtained at the node 2N8. Yet, thetransistor may be turned ON and OFF by an integrated circuit IC.

FIG. 19B is a circuit diagram of a lamp 271 including a lighting unit273 according to the modification 5 of the present invention.

As illustrated in FIG. 19B, the lamp 271 according to the modification 5includes a light-emitting unit 243 and a lighting unit 273 for operatingthe light-emitting unit 243. Similarly to the third embodiment, thelight-emitting unit 243 includes a plurality of LEDs and is identical instructure to the light-emitting unit according to the modification 4.

The lighting unit 273 includes a rectifier circuit 251, a smoothingcircuit 253, a starting circuit 275, and a feed circuit 277. Therectifier circuit 251 and the smoothing circuit 253 are identical instructure to the rectifier circuit and the smoothing circuit accordingto the third embodiment.

The feed circuit 277 includes an FET 2Q4 acting as a switching elementand a choke coil 2L2 for driving an integrated circuit 21C that adjuststhe ON state of the FET 2Q4.

The starting circuit 275 includes the integrated circuit 21C for judgingwhether a predetermined condition is satisfied or not. Morespecifically, three resistors 2R6, 2R7, and 2R8 are serially connectedvia nodes 2N9 and 2N10. The serial resistors 2R6, 2R7, and 2R8 areconnected in parallel to the smoothing circuit 253.

The integrated circuit 21C measures the voltage at the nodes 2N9 and2N10. When the voltage at the node 2N10 reaches a predetermined value,the integrated circuit 21C turns ON the FET 2Q4.

Similarly to the modification 4 described above, the specifications ofthe resistors 2R6, 2R7, and 2R8 and the integrated circuit 21C of thelighting unit 273 according to the modification 5 are so determined thatthe FET 2Q4 is not turned ON when the source voltage Vs is 120V.

<Supplemental Note>

1. Lighting Unit

The lighting units 7 and 103 according to the first embodiment and thesecond embodiment 1, respectively, are for lighting the arc tube 3. Onthe other hand, the lighting unit 203 according to the third embodimentis for lighting the light-emitting unit 205 composed of LEDs.

However, it is applicable that the lighting units 7 and 103 are modifiedto light the light-emitting unit according to the third embodiment.Similarly, the lighting unit 203 may be modified to light the arc tubeaccording to the first embodiment and second embodiment 1.

Naturally, when making such a modification to the lighting units, it isnecessary to change the specifications of the electronic components ofthe lighting units.

2. Partial Smoothing Circuit

The smoothing circuit is not limited to the circuit 53 described in thefirst embodiment. Any smoothing circuit is applicable as long as aplurality of smoothing capacitors are included and the smoothingcapacitors are connected to be in series at the time of charging and inparallel at the time of discharging. The following describesmodifications 6-8 directed to partial smoothing circuits havingdifferent structures.

(1) Modification 6

FIG. 20A is a circuit diagram of a smoothing circuit 301 according to amodification 6 of the present invention.

The parietal smoothing circuit 301 according to the modification 6includes three smoothing capacitors 3CD1, 3CD2, and 3CD3 and six diodes3D1, 3D2, 3D3, 3D4, 3D5, and 3D6.

The three smoothing capacitors 3CD1, 3CD2, and 3CD3 are seriallyconnected via diodes 3D2 and 3D5 placed between each two capacitors. Thediodes 3D2 and 3D5 are connected so that the forward direction coincideswith the direction from the positive terminal toward the negativeterminal of the rectifier circuit.

The cathode terminal of the diode 3D1 is connected between the smoothingcapacitor 3CD1 and the diode 3D2. The cathode terminal of the diode 3D4is connected between the smoothing capacitor 3CD2 and the diode 3D5.

The diodes 3D1 and 3D4 are connected, so that the forward directioncoincides with the direction from the negative terminal of the rectifiercircuit toward the smoothing capacitors 3D1 and 3D2. In addition, theanode terminals of the respective diodes 3D1 and 3D4 are connected tothe negative terminal of the rectifier circuit.

In addition, the anode terminal of the diode 3D3 is connected betweenthe diode 3D2 and the smoothing capacitor 3CD2. The anode terminal ofthe diode 3D6 is connected between the diode 3D5 and the smoothingcapacitor 3CD3.

The diodes 3D3 and 3D6 are connected, so that the forward directioncoincides the direction from the smoothing capacitors 3D2 and 3D3 towardthe positive terminal of the rectifier circuit. In addition, the cathodeterminals of the respective diodes are connected to the positiveterminal of the rectifier circuit.

With the above-described connection, the smoothing capacitors 3CD1,3CD2, and 3CD3 are placed in series at the time of charging. On theother hand, at the time of discharging, the serially connected smoothingcapacitor 3CD1 and diode 3CD1 are, the serially connected diode 3D3,smoothing capacitor 3CD2, and diode 3D4, and the serially connecteddiode 3D6 and smoothing capacitor 3CD3 are placed in parallel.

With this connection, the first voltage value V1 of the smoothed voltagebecomes one-third of the second voltage value V2 shown in FIG. 5.

(2) Modification 7

FIG. 20B is a circuit diagram of a partial smoothing circuit 303according to a modification 7 of the present invention.

The partial smoothing circuit 303 according to the modification 7includes four smoothing capacitors 3CD4, 3CD5, 3CD6, and 3CD7 as well asfive diodes 3D7, 3D8, 3D9, 3D10, and 3D11.

The smoothing capacitors 3CD4 and 3CD5 are serially connected via thediode 3D8. Here, the cathode terminal of the diode 3D8 is connected tothe smoothing capacitor 3CD5. The smoothing capacitors 3CD6 and 3CD7 areserially connected via the diode 3D10. Here, the cathode terminal of thediode 3D10 is connected to the smoothing capacitor 3CD7.

In addition, the diode 3D9 connects a node between the seriallyconnected diode 3D8 and smoothing capacitor 3CD5 with a node between theserially connected smoothing capacitor 3CD6 and diode 3D10. Here, thecathode terminal of the diode 3D9 is concocted to the diode 3D10.

In addition, a node between the smoothing capacitor 3CD4 and the diode3D8 is connected to the cathode terminal of the diode 3D7. The diode 3D7is so connected that the forward direction coincides with the directionfrom the negative terminal of the rectifier circuit toward the smoothingcapacitor 3CD4. Here, the anode terminal of the diode 3D7 is connectedto the negative terminal of the rectifier circuit.

In addition, a node between the diode 3D10 and the smoothing capacitor3CD7 is connected to the anode terminal of the diode 3D11. The diode3D11 is so connected that the forward direction coincides with thedirection from the smoothing capacitor 3CD7 toward the positive terminalof the rectifier circuit. Here, the cathode terminal of the diode 3D11is connected to the positive terminal of the rectifier circuit.

With the above-described connection, at the time of charging, thesmoothing capacitors 3CD4 and 3CD5 are in series and the smoothingcapacitors 3CD6 and 3CD7 are in series.

On the other hand, at the time of discharging, discharge occurs in aseries circuit composed of the diode 3D7 and the smoothing capacitor3CD4, a series circuit composed of the smoothing capacitor 3CD6, thediode 3D9, and the smoothing capacitor 3CD5, and a series circuitcomposed of the smoothing capacitor 3CD7 and the diode 3D11.

With this arrangement, the first and second voltage values V1 and V2 ofthe smoothed voltage are in the same relation to those illustrated inFIG. 5. Yet, the rate at which the voltage varies between the first andsecond voltage values can be made slower.

(3) Modification 8

FIG. 20C is a circuit diagram of a partial smoothing circuit 305according to a modification 8 of the present invention.

The partial smoothing circuit 305 according to the modification 8includes two smoothing capacitors 3CD8 and 3CD9, three diodes 3D12,3D13, and 3D14, and one resistor 3R1.

The two smoothing capacitors 3CD8 and 3CD9 are serially connected viathe diode 3D13 and the resistor 3R1. The forward direction of the diode3D13 coincides with the direction from the positive terminal towardnegative terminal of the rectifier circuit.

A node between the smoothing capacitor 3CD8 and the diode 3D13 isconnected to the cathode terminal of the diode 3D12. The forwarddirection of the diode 3D12 coincides with the direction from thenegative terminal of the rectifier circuit toward the smoothingcapacitor 3CD8. In addition, the anode terminal of the diode 3D12 isconnected to the negative terminal of the rectifier circuit.

A node between the resistor 3R1 and the smoothing capacitor 3CD9 isconnected to the anode terminal of the diode 3D14. The forward directionof the diode 3D14 coincides with the direction from the smoothingcapacitor 3CD9 toward the positive terminal of the rectifier circuit. Inaddition, the cathode terminal of the diode 3D14 is connected to thepositive terminal of the rectifier circuit.

With the above-described connection, at the time of charging, thesmoothing capacitors 3CD8 and 3CD9 are in series. At the time ofdischarging, on the other hand, the serially connected smoothingcapacitor 3CD8 and diode 3D12 and the serially connected smoothingcapacitor 3CD9 and diode 3D14 are placed in parallel.

With this arrangement, the first voltage value V1 of the smoothedvoltage illustrated in FIG. 5 is expressed as follows:V1=(V2−Vr)/2

Here, Vr denotes the voltage of the resistor 3R1.

3. Supplemental Note

According to the second embodiment 1, the lighting unit has a shortcircuit placed at one of the electrodes of the arc tube and a negativetemperature coefficient resistor NTC is connected in parallel to theother electrode. Yet, it is applicable that none of the abovearrangements is made to the electrodes. In this case, a large electriccurrent flows through the filament coils during the lamp operation.Consequently, flickering of the lamp that occurs when the source voltageVs is 120V is less noticeable (unilluminated periods are shorter). Yet,the flickering is still noticeable to human eye, so the effect iscomparable to that of the second embodiment 1.

Instead of the negative temperature coefficient resistor NTC, a positivetemperature coefficient resistor PTC may be connected in parallel to thearc tube. In this case, at the time of power ON, preheating currentflows through the electrodes (filament coils). Thus, the flickering ofthe lamp that occurs when the source voltage Vs is 120V is lessnoticeable. Yet, the circuit operations tend to stabilized more easily,so that damage to the circuits and the arc tube caused at the time ofmisuse is kept to a minimum.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless such changes and modifications depart fromthe scope of the present invention, they should be construed as beingincluded therein.

Those skilled in the art will appreciate that various adaptations andmodifications of the just-described preferred embodiment can beconfigured without departing from the scope and spirit of the invention.Therefore, it is to be understood that, within the scope of the amendedclaims, the invention may be practiced other than as specificallydescribed herein.]

What is claimed is:
 1. A lamp with a rated voltage of 277 volts,comprising: a light-emitting unit including one or more light-emittingdiodes; and an electronic lighting circuit including: a lighting unitoperable to cause the light-emitting unit to illuminate in a manner tovisually indicate to a user that the illumination is normal, when aneffective source voltage of 277 volts is supplied; and a lightingcontrol unit operable to cause the light-emitting unit to flash on andoff, when an effective source voltage of 120 volts, which is differentfrom the rated voltage, is supplied.
 2. The lamp according to claim 1,wherein the lighting unit includes a switching element operable to startpower feed to the light-emitting unit, and wherein the lighting controlunit includes a starting circuit operable to cause the switching elementto turn on, when an input signal to the starting circuit reaches athreshold, wherein the input signal includes ripple components, andwherein the threshold is (i) smaller than a minimum value of the signalinput when the effective source voltage of 277 volts is supplied and(ii) between a minimum value and a maximum value of the signal inputwhen the effective source voltage of 120 volts is supplied.
 3. The lampaccording to claim 2, wherein the light-emitting unit includes aplurality of light emitting diodes that are serially connected into aplurality of arrays such that the light-emitting diodes in each arrayhave a same forward direction, wherein the plurality of arrays includesarrays having mutually opposite forward directions, and wherein thelighting unit is operable to supply alternating current voltage to thelight-emitting unit.
 4. The lamp according to claim 2, wherein thelight-emitting unit includes the plurality of light-emitting diodes,LEDs that are serially connected into a single array such that thelight-emitting diodes in the array have a same forward direction, andwherein the lighting unit is operable to supply direct current voltageto the light-emitting unit.
 5. The lamp according to claim 2, whereinthe electronic lighting circuit further includes: a rectifier circuitoperable to rectify alternating current voltage from a commercial powersource; and a smoothing circuit operable to smooth an output voltage ofthe rectifier circuit, wherein the smoothing circuit is an electrolyticcapacitor, and the ripple components are present in an output voltage ofthe smoothing circuit.
 6. The lamp according to claim 5, wherein thelighting control unit includes an adjusting circuit operable to causethe switching element having been turned on by the starting circuit toturn on and off according to an electric current flowing through thelighting unit.
 7. The lamp according to claim 1, wherein the electroniclighting circuit further includes: a rectifier circuit operable torectify alternating current voltage from a commercial power source; anda smoothing circuit operable to smooth an output voltage of therectifier circuit, wherein the lighting unit includes a switchingelement operable to start power feed to the light-emitting unit, andwherein the lighting control unit includes a starting circuit operableto turn on the switching element, when an input signal reaches athreshold, wherein the smoothing circuit is a partial smoothing circuitoperable to output a voltage maintained at a predetermined voltage valueeven when the output voltage of the rectifier circuit becomes lower thanthe predetermined voltage value, and wherein the predetermined voltagevalue is lower than the threshold at a time when the effective sourcevoltage of 120 volts is supplied and is higher than the threshold at atime when the effective source voltage of 277 volts is supplied.
 8. Thelamp according to claim 6, wherein the adjusting circuit is a choke coilincluding: a primary coil connected in series with the lighting unit;and a secondary coil magnetically coupled to the primary coil.
 9. Thelamp according to claim 8, wherein the switching element is atransistor, and wherein the secondary coil is connected to a base and anemitter of the transistor.
 10. The lamp according to claim 8, whereinthe switching element is a field effect transistor element, wherein thestarting circuit is an integrated circuit, and wherein the secondarycoil is connected to a power supply terminal of the integrated circuitand a source of the field effect transistor element.
 11. A lamp with arated voltage of 277 volts, comprising: a light-emitting unit includingone or more light-emitting diodes; and an electronic lighting circuitincluding: a lighting unit operable to cause the light-emitting unit toilluminate in a manner to visually indicate to a user that theillumination is normal, when the lamp is used by being connected to a277 volt distribution line; and a lighting control unit operable tocause the light-emitting unit to flash on and off, when the lamp is usedby being connected to a 120 volt distribution line, which is differentfrom the 277 volt distribution line.
 12. The lamp according to claim 11,wherein the light-emitting unit includes a switching element operable tostart power feed to the light-emitting unit, wherein the lightingcontrol unit includes a starting circuit operable to cause the switchingelement to turn on, when an input signal to the starting circuit reachesa threshold, wherein the input signal includes ripple components, andwherein the threshold is (i) smaller than a minimum value of the signalinput when the effective source voltage of 277 volts is supplied and(ii) between a minimum value and a maximum value of the signal inputwhen the effective source voltage of 120 volts is supplied.
 13. The lampaccording to claim 11, wherein the electronic lighting circuit furtherincludes: a rectifier circuit operable to rectify alternating currentvoltage from a commercial power source; and a smoothing circuit operableto smooth an output voltage of the rectifier circuit, wherein thelighting unit includes a switching element operable to start power feedto the light-emitting unit, and wherein the lighting control unitincludes a starting circuit operable to turn on the switching element,when an input signal reaches a threshold, wherein the smoothing circuitis a partial smoothing circuit operable to output a voltage maintainedat a predetermined voltage value even when the output voltage of therectifier circuit becomes lower than the predetermined voltage value,and wherein the predetermined voltage value is lower than the thresholdat a time when the effective source voltage of 120 volts is supplied andis higher than the threshold at a time when the effective source voltageof 277 volts is supplied.